The recent development of fluid mechanics in the field of fluid power engineering is surveyed. Topics covered include unsteady flow in pipelines, unsteady flow measurement, cavitation in unsteady flow, flows in fluid power components, and flow-induced vibrations.

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The pressure response of a small air bubble in water is calculated numerically in an oscillatory pressure field. Many phenomena are taken into account in the calculation, such as mist formation inside the bubble due to homogeneous condensation, and the diffusion between vapor and noncondensable gas inside the bubble. The internal condition adapts itself easily to the oscillatory pressure field by the internal phenomena, which include mist formation, and evaporation and deposition onto the bubble wall, so that the bubble tends to oscillate synchronously. The frequency response curves for bubbles are calculated. The curve is shifted toward the lower frequency and the maximum bubble radius becomes larger. When the pressure amplitude is increased, the periodic bubble oscillation bifurcated to a nonperiodic oscillation which constitutes a deterministic chaos.

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This paper deals numerically with the nonlinear oscillations of two spherical gas bubbles interacting in a sound field. The nonlinear oscillations of the bubbles are investigated for different pressure amplitudes of the sound field and for different equilibrium radii of the bubbles. It is shown that the interaction effect becomes prominent in the frequency response curves of an initially smaller bubble; these curves are different from those of a single bubble. The harmonic resonance of the initially smaller bubble is more easily destroyed than that of the single bubble. The results also show that once one bubble begins the ultraharmonic oscillation, the second bubble also begins the ultraharmonic oscillation. This suggests that both bubbles can be the source of the first subharmonic component in the acoustic cavitation noise.

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Turbulence generated near the wall of a pipe propagates in both the radial and the axial directions. Compared to axial propagation, knowledge of radial propagation is very limited. This investigation is intended to clarify the radial propagation of wall turbulence in pulsatile turbulent pipe flows. It becomes evident that the turbulence is mainly generated around y⁺=20 and propagates toward the wall as well as the pipe center, where y⁺=yu^^-_{*, ta}/ν, y the distance from the wall, u^^-_{*, ta} the time-averaged friction velocity, and ν the kinematic viscosity. The propagation time near the generation region scales well with inner variables, u^^-_{*, ta} and ν, whereas in the central part of the pipe it scales with u^^-_{*, ta} and the pipe radius R. Empirical expressions for the propagation time are derived, and models for Reynolds shear stress and eddy viscosity are proposed.

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Various conditional statistics have been examined for the turbulent diffusion of dye solution from a continuous point source in a uniform mean shear flow. The conditional sampling technique consists of two steps: the first step A, which determines the intermittency factor from the probability density function; and the second step B, at which the intermittency function by using a threshold level and a hold time are obtained. It is shown that the transverse profiles of the intermittency factor, the zone-averaged mean concentration and the zone-averaged concentration fluctuation r.m.s. value are all asymmetric about the center line of the plume. The new dimensionless diffusion time η is introduced in terms of the r.m.s. value and the integral length scale of longitudinal velocity fluctuation, and the relative decay rates along η of these conditional statistics on the center line of the plume are estimated and compared with the results in grid-generated turbulent flow.

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The regions and mechanism of cavitation noise generation on the surface of an axial-flow pump impeller were clarified based on detailed studies, under various cavitation conditions, of pressure fluctuation levels along the impeller casing, inclusive of the outlet side away from the impeller. The region influencing cavitation noise generation the most was found to be less than approx. 1/3 of the chord extending from the leading edge of the impeller blades. A great difference existed in the pressure between the two-phase flow, comprised of vapor bubbles formed in the impeller tip zone, and the main flow, causing an increase in the levels of high-frequency pressure fluctuation components due to cavitation. This indicates that the above two-phase flow has a great influence on cavitation noise generation. This paper also discusses the process of transition from pressure fluctuation to air-borne noise.

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Speed-dependent characteristics of centrifugal fan noise are discussed by introducing a model of wave transmission through the impeller and the inlet duct. The fan noise data at the inlet are categorized as source strength terms and a frequency-response term expressing attenuation in the propagation passage. By setting the exponent in a power-law relationship of the 2 nd power of sound pressure level versus frequency at 6, i.e., a dipole source, two factors describing the source level are determined with simple relationships to the cut off clearance. The frequency response is satisfactorily predicted by introducing a one-dimensional linear wave model in which the key passage is the blade-to-blade passage selectively determined by the noise wavelength. Through selection of the blade number or the inlet duct length so that the frequency of the maximum attenuation is achieved, the fan noise level is reduced by more than 10 dB, without any influence on fan performance.

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An oil system is the equipment used to control the flow of hydraulic oil to the bearings and seals in process compressors and steam turbines. Conventional oil systems, in many cases, are controlled by pneumatically operated process control valves. It is generally difficult, however, to control the relatively rapid response of an oil hydraulic system by a pneumatically operated control system. A new type of control valve for header pressure control was therefore developed. The dynamic characteristics of the oil system using the new type of valve were examined theoretically and experimentally. The effect of parameter variation on the pressure response and stability of the control valve was clarified. The result was that the stable region of this system increased with an increase in the valve flow force.

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This paper describes an experimental study of the dynamic fluid reaction force which is generated in the axially long annular clearance between the rotor and stator of a submerged motor pump or in the balance piston of a turbo pump where fluid flows axially. For measuring the dynamic fluid force, a test rig was made to demonstrate the spin and whirl motion of the rotor. In the test, the rotor and the stator were set in the concentric condition and the pressure fluctuation, fluid reaction force and flow rate were measured under the basic parameters of rotational speeds and pressure drop across the long seal. The tangential force component was obtained from the dynamic fluid force and the instability threshold (limit) was determined. In addition, the dynamic fluid force was expressed in terms of the stiffness coefficient, damping coefficient and added mass; each coefficient is discussed in detail in this paper.

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In treating problems of thermal conduction in dispersive media, it is necessary to calculate the effective thermal conductivity instead of analyzing the detailed thermal field. The present paper aims to estimate the effective thermal conductivity of two-dimensional media with regularly dispersed materials by applying the boundary element method. Media with parallel cylinders dispersed at square lattice points are considered. It is assumed that two-dimensional thermal conduction takes place in the plane normal to these cylinders. In the case of regularly arranged circular cylinders, the present authors have also developed an exact analytical method. The preaent method is compared with the previous one by carrying out numerical calculation and the result is satisfactory. The method is also applied to analyze the case of cylinders of square cross section.

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The purpose of this report is to investigate the fluid flow and heat transfer in an opposed plane jet in a uniform stream. In the previous paper, experimental results indicated that there were unsteady motions of low frequency and large scale, which are known as jet flapping. In the present paper, the unsteady motions for the Reynolds number of a jet, Re₀=1500, and the ratio of the jet to uniform stream velocity, α=3.75, are studied numerically by the finite difference method. Previous experimental results are simulated in outline by numerical calculations. Time histories and instantaneous or time-averaged contours for velocity, pressure coefficient and temperature are obtained, and the mechanisms of fluid flow and heat transfer are clarified.

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The heat transport characteristics of a thermosyphon are investigated experimentally using R 113, methanol, and water as the working fluids. The condensation heat transfer coefficient of the cooling section shows a trend to decrease with increasing wall temperature difference .This trend is similar to Nusselt's prediction. However, its value is considerably lower under the condition of high vapor velocities. Based on the heat transfer characteristics of the heating and cooling sections, nondimensional expressions are derived to relate the heat transport rate to the temperature difference between the heating and cooling sections .These expressions are compared satisfactorily with the measured results.

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In order to measure the transient temperature of gas, a laser interferometry was applied. When the density of gas changes, the effective optical path length of the test beam changes with a corresponding change of the refractive index. The change in temperature of the gas therefore can be determined by measuring the pressure and the shift of the interference fringes with a pair of phototransistors. In this study, examples of the temperature change measurement of the gas owing to only the expansion, to the compression and expansion with a piston motion, and to the compression with flame propagation were described. It is recognized that interferometry is a useful method for the measurement of the transient temperature of the gas in the field of combustion research.

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An experimental study was carried out on the excess enthalpy burning of an ultralean-methane/air mixture using a heat- recirculating burner. The flame-stability limit, the gas temperatures and the chemical composition of the burnt gas were examined, while the flame behavior was carefully observed. The conclusions obtained were as follows : (1) Almost completely burnt gases are produced with a negligibly small amount of nitrogen oxide. (2) If the combustion of the mixture is incomplete in the combustion chamber and the residual of the mixture burns secondarily in the hot part of the heat exchanger downstream of the combustion chamber, the temperatures of both the preheated mixture and the flame drop. (3) The flame blows off prior to the approach to the proper limit of flammability for the preheated mixture, and flame stabilization in the combustion chamber is important since the mixture at the blowoff limit is still flammable.

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The instantaneous spatial temperature profile is measured by the laser Rayleigh scattering method using a detector which has 512 photodiode elements in a single line. The detector was applied to two typical turbulent diffusion flames with different degrees of turbulence. The results obtained are as follows. (1) A comparatively large-scale temperature fluctuation dominates the temperature fluctuation intensity in turbulent diffusion flames. (2) The average and instantaneous maximum temperature tends to decrease when the Reynolds number increases ; consequently the turbulence tends to increase.

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The combustion characteristics of single CWM and COM droplets on a hot surface were investigated. The surrounding temperature was carefully adjusted to the temperature of the hot surface. The vaporization and combustion behavior of a single slurry droplet under a uniform temperature condition could then be observed. The ignition delay time of the COM droplet was shorter than that of the CWM droplets. When the initial diameter of the droplet decreased, the total burning time decreased proportionately with the square of the initial diameter. The effect of the size distribution of the pulverized coal appeared on the lower temperature limit of the surface reaction process of the fixed carbon. Ten kinds of pulverized coal were compared to obtain the relation between the fuel ratio of the coal and the apparent diffusion coefficient that controlled the combustion of the slurry droplet.

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The sooting process occurring during combustion of a mixture of gaseous fuel and air is described by a theory based on homogeneous nucleation. This theory includes the concepts of carbon cluster kinetics and partial equilibrium to permit description of a slow chemical step such as the thermal decomposition of raw fuel. The likelihood of homogeneous nucleation in sooting is shown from a thermodynamical aspect taking the Gibbs free energy of each intermediate product into consideration. The predicted results of the proposed theory are compared with results obtained from shock-tube experiments and steady-flow reactor experiments. It is suggested that clustering may result in the rapid formation of soot, despite very low carbon vapor concentration, and that there is a cluster class above which the soot mass yield remains unchanged. Furthermore, it is suggested that the strong temperature dependence of soot yield in a very fuel-rich mixture stems from a low carbon vapor concentration at lower temperatures and a high rate of declustering reactions at higher temperatures.

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The total directional and hemispherical emittances of an isothermal layer of dispersed soot particles are evaluated theoretically by solving the spectral equation of radiation transfer over the wavelength region from 0.4 to 100 μm and the effects of the kinds of soot, layer thickness, particle diameter and temperature on the total slab emittance are revealed. The Rayleigh approximation to the total slab emittances are also examined. it was found that the total directional and hemispherical emittances are barely affected by the kinds of soot and that the Rayleigh approximation is valid for a layer of soot particles less than about 0.1 μm in diameter.

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The effect of the H/C weight ratios of pyrolytic graphite, acetylene and propane soots on their dispersion parameters are discussed quantitatively. The dispersion parameters are determined by analyzing the previously reported data for the normal reflectances of these materials based on the many bound-electron model. The total normal emissivities of soot particles are calculated utilizing the dispersion parameters thus determined.

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