This paper outlines some of the developments in fluid power technology to overcome the challenges posed by other forms of energy transmission. It is shown that many of these advances are associated with the incorporation of electronic devices, microprocessors and the application of modern control techniques as well as improvements in fluid power components. A central issue is the reduction of pump flow-ripple in order to reduce system vibration and noise. Other environmental factors are also discussed.

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The current status of field modelling of tire spread in compartment fires is reviewed in terms of the recent development of field models. Emphasis is placed on the development of several critical submodels for turbulence, thermal radiation, turbulent combustion, and also for handling complex compartment geometries, as well as on the validation of the field models with experimental data based on full-scale fire tests. The shortcomings of the current field models and critical research needs are then identified and discussed.

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A study has been made of turbulent vortices behind various wake-generating bodies (circular, triangular and square cylinders and a screen of 50% solidity). Using a rake of eight X-probes which was aligned in the plane of mean shear, velocity data have been obtained in the far wake at sufficiently large Reynolds numbers. Profiles of the Reynolds stresses show measurable differences in the wakes from different generators. Correspondingly, some aspects of the organized motion, e.g., the circulation of the vortices and their coherent contributions to the Reynolds stresses, are sensitive to the initial conditions. The difference is especially noticeable between the wake of the screen and the solid-body wakes. For the screen, the far-field vortices are highly similar to the near-field ones. For the solid-body wakes, the far-field vortices bear little resemblance to the near-field vortices.

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To predict the behavior of air-water two-phase flows in centrifugal pumps, we have proposed a three-dimensional numerical method on the basis of an inviscid bubbly flow model with slippage between two phases. The void fractions calculated distribute unevenly and their maximum exceeds an applicability of the model. To extend its applicability, a newly modified model is proposed in this paper by assuming that the bubbles in such high void fraction regions coalesce with each other and adhere to the neighboring impeller walls so as to form a fixed cavity. Using this model, the flows in a radial-flow pump are solved. The cavity obtained increases progressively from the shroud to the hub in the section just after the impeller inlet when the inlet void fraction exceeds a critical value and finally fills the section, showing close relation with the experiments when the pump loses its function due to an air-filled blockade.

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The motion of a single bubble is simulated when the surrounding pressure decreases stepwise. In this simulation, the conservation equations for mass, momentum and energy are solved directly in order to estimate the effect of internal phenomena on bubble motion. At the same time, the mist formation in the gas phase and the diffusions of heat and noncondensable gas in the liquid phase are taken into account. The numerical results for several cases reveal that nondimensional transport coefficients have large effects on the distributions of temperature, concentration of vapor and the mist formation. As the initial radius becomes smaller or depressurization ratio becomes larger, bubble motion is less influenced by mist formation due to the heat penetration through the bubble wall by heat conduction.

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In order to improve the reliability of butterfly valves, it is absolutely imperative to prevent fatal cavitation erosion and to control the flow rates precisely. In our previous studies, erosive vortex cavitation, which takes place within a limited part of the high-shear region, was found to play an important role in the erosion. This fact suggests to us a useful method for overcoming erosion. To date, many types of modified valves have been proposed, in which very uniquely-shaped buffers are attached on the orifice and nozzle sides of the valve disc, although data on the results of their practical use are unavailable. In this paper, therefore, the erosive shock-pressure distributions on the inner pipe-wall surface downstream from the valve disc and the corresponding cavitation-flow pattern are precisely measured in the typical bounded flow around butterfly valves by means of pressure-sensitive films and high-speed photography. It is found that the erosive pulses and the range of their occurrence in the shear regions can be significantly attenuated by introducing simple buffers.

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The effects of area ratio on electrical and fluid-dynamical properties in a disk magnetohydrodynamic (MHD) generator have been experimentally investigated. The experimental results have shown that for a generator with a large area ratio, the wall static pressure is kept lower than that of a small-area-ratio generator. It is observed that high values of the Hall electric field are obtained at the downstream part of a channel with large area ratio. The stagnation pressure at the exit of the disk MHD channel was measured and compared with the results of one-dimensional calculations. It was found that in pressure loss processes a strong Lorentz force becomes quite significant relative to wall friction which plays a major part in the pressure loss mechanism in the absence of MHD interaction.

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The purpose of this work is to predict analytically the unsteady loading on vibrating blades of a supersonic through-flow fan and conduct the parametric study of the aerodynamic instability. A linearized unsteady lifting surface theory on the basis of the finite radial eigenfunction series approxmation is developed. It is assumed that each blade vibrates with a small displacement amplitude under zero mean loading. Numerical results for pure bending, pure torsional and combined bending and torsional vibrations are presented to demonstrate influences of interblade phase angle, location of torsion axis, axial Mach number and reduced frequency on the aerodynamic instability of blade motions.

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Flow behavior of underexpanded coaxial impinging jets is investigated experimentally and simulated numerically by solving compressible Navier-Stokes equations. Two converging coaxial nozzles, one with outer annular jet parallel to an inner circular one, and the other with inclined annular jet, are fabricated and tested. The flow visualization using the shadowgraph method, the pressure measurements at the impinged surface and the numerical simulation show that the presence of the outer annular jet has favorable effects for reducing the diameter of the Mach shock disk which is formed in the inner jet. However, the maximum pressure on the impinged flat plate obtained in the present study is lower than that produced previously by a simple annular jet, showing that the simple annular jet can be more favorable for laser cutting.

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The switching mechanisms in devices such as wall attachment fluid amplifiers, turbulence amplifiers and beam deflection amplifiers have excellent properties, and many investigations have been reported. In turbulent opposed jets, it is found that the impact position can be controlled by turbulence in the jet center. In this paper, the performance of a new fluidic amplifier applied to the above-mentioned phenomenon is described. The new fluidic amplifier consists of an outer pipe, two opposed nozzles, a small nozzle to generate control flows and a separator. The impact position generated by the opposed jets is controlled by the small control flow by way of the small nozzle. The new fluidic amplifier can be driven by small control flow, and as a result, is a useful component in a complex circuit.

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The statistical properties of a periodically diverging-converging turbulent channel flow are examined experimentally. Air flow is alternately decelerated through a linearly diverging section, and accelerated through a converging section. Measurements on the energy spectrum, auto-correlation, probability density, skewness/flatness factors and space-time correlation are made in two channels with different diverging-converging angle. The inertial subrange can be recognized for the diverging and converging sections. Large differences are observed in the skewness and flatness factors compared with the equilibrium turbulent flows with no pressure gradient. The eddy scales in the converging section are considerably smaller than those in the diverging section.

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This paper describes air-entraining vortices generated when water is drained from a vessel. The liquid used in this experiment is a mixture of water and bentonite. By changing the mixing ratio, the coefficients of kinematic viscosity of the liquid were changed to six values ranging from 0.0105 to 0.0625 cm²/s. Air-core vortices and vortices without air core are not generated in liquid deeper than a certain depth. Within the scope of this experiment, this depth increased with the increase of flow quantity. Also, it was found that vortices were not generated at radial Reynolds number R_r, derived from the equation of motion, lower than a certain value. For example, in liquids having the coefficients of kinematic viscosity ν=0.0105 and 0.0652cm²/s, air-entrained vortices are not generated at R_r<3000 for the former and R_r<800 for the latter. Although the inner diameters of effluent pipes were 2.03, 3.23, and 5.15 cm, effects of the difference were rarely found. However, it was found that the values of R_r in this limit were reduced as the viscosity of liquids increased.

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As the first step in systematic research on decelerating unsteady boundary layers, the fundamental problem of the unsteady laminar boundary layer on a linearly retarded semi-infinite flat plate has been analyzed theoretically. Precise solutions for the flow characteristics are obtained by means of a series expansion technique and a numerical analysis. In addition, an original semi-quantitative "viscous diffusion theory" has been developed, and the physical mechanism and structure of flow behavior in the boundary layer, which cannot be explained well by any existing numerical or similar quantitative-oriented methods, have been analyzed phenomenally and are clarified satisfactorily by this new theory.

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In the present work, structures and time-averaged flow properties in the transition region of a plane wake perturbed by the unstable subharmonic modes were studied by means of direct numerical simulations. The incompressible time-dependent 2-D Navier-Stokes equations were solved using Pade finite difference approximations in the streamwise direction, a mapped pseudospectral Fourier method in the cross-stream direction, and a third-order compact Runge-Kutta scheme for time advancement. The unstable modes (fundamental mode and its subharmonics) of the Orr-Sommerfeld equations were used to perturb a Gaussian wake of the inlet plane. The statistics of the wake forced by the unstable modes and the corresponding numerical structures of the vortices are presented. When the wake is forced by the fundamental mode and its two subharmonics with large amplitudes, the dominant evolution of the fundamental mode is responsible for the clear alternating sign vortices and the downstream statistics. After the fundamental mode saturates, the subharmonic components grow downstream. Further downstream, the influence of the first subharmonics on the vortex street and the turbulent statistics are observed. The downstream evolutions of Reynolds stresses are governed by the growth of the subharmonics. The cross-stream profiles of the Reynolds stresses are asymmetric because of the spatial evolution of the first subharmonics.

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The vortex blob model, which is one of the previously proposed vortex models in the vortex method, was modified to correctly take account of the viscous effect with a simpler procedure of calculation. To examine the usefulness of the modified model, the interaction of two vortex rings is calculated with it and two other vortex models ; the filament model and the vorton model. As a result of the comparative calculation, it was confirmed that not only the process of connecting the two rings into a single ring at an early stage of interaction, but also the process of splitting the single ring into two rings at the following stage was reasonably simulated by the modified model.

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The SOLA (solution algorithm) method is one of the most widely used methods for analyzing incompressible flows. However, this method often requires a number of iterations to obtain a converged solution for a practical problem on transient flow. Hence, a theoretical analysis of this method was carried out in the present study to clarify the reason why this method can give converged solutions. It was proven that the SOLA method is identical to the SMAC (simplified marker and cell) method for the interior cells of the computational domain. On the other hand, it is not identical to the SMAC method for the cells adjacent to the boundary cells. Hence, a modified SOLA method which improves computational efficiency was developed by taking into account boundary conditions in the iteration process. It was demonstrated that the modified SOLA method could analyze transient flow more efficiently than the original SOLA.

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A numerical technique for investigating the mixing characteristics of supersonic turbulent flow with different gas species, in which a two-equation turbulence model was employed, was presented in the first report. This report clarifies the effect of inlet flow profiles on the mixing phenomena by adopting distributed flow profiles obtained for a supersonic wedge-shaped nozzle outlet as the inlet boundary conditions for the mixing calculations. The general conclusion is that mixing layers with distributed inlet flow profiles are thicker than those with uniform profiles. Furthermore, the relationships of the growth rates of mixing layers with distributed inlet flow profiles to the changes in the velocity ratios and density ratios are similar to those of layers with uniform profiles.

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This study is a direct numerical simulation of a spatially evolving reactive mixing layer of a hydrogen/air system. A second-order TVD scheme with full chemical mechanism was employed to observe the mixing and ignition process. Mixing efficiency and ignition location were investigated under different convection Mach numbers. Techniques for enhancing ignition are discussed, attention being given to the coupling of the shear layer growth rate and viscous dissipation. Results show that an increase of convective Mach number significantly decreases fuel-air mixing efficiency, but enhances the viscous dissipation. As a result, a decrease of shear layer thickness enhances the auto-ignition at high Mach numbers. It was also found that an increase of hydrogen velocity causes the shear layer to shift toward the air side, leading to a shorter ignition delay time. Furthermore, the effect of instability of the shear layer on ignition was also investigated. It was found that an improvement of ignition was-achieved by imposing a very small perturbation upstream.

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Experimental investigations into an affinity law of cross-flow fans have been conducted using three fans of different sizes but good geometrical similarity, and anomalous scale effects appearing on the performance curves have been shown. The results obtained have been confirmed with a series of additional experiments which examine the effects of errors of geometrical configurations of tested fans, as well as effects of the flow turbulence and velocity distributions of the inlet flow into the fans. The critical Reynolds number based on the chord length and tip speed of the rotor is as small as (1.0∼1.5)×10⁴. The performance curves represented in a conventional nondimensional form are affected by Reynolds number as well as the fan dimensions, which shows that the performances of cross-flow fans never simply obey the conventional affinity law of fans, hence it is essential to introduce the fan dimensions to represent the performance in a general form.

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In order to predict performances of mixed-flow pumps over the whole discharge range, it is necessary to establish a calculation method of theoretical head and power loss caused by a reverse flow at the inlet and the outlet of an impeller. In this report, a reverse flow model at an impeller inlet is proposed together with the dependence of the slip factor upon discharge, and a prediction method of theoretical head and water power of mixed-flow pumps by a simple calculation is presented using this inlet reverse flow model. The comparison with the measurements revealed that the present method yields a good prediction for the inlet velocity distribution and for the theoretical head and water power in the whole discharge range.

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The flow field at the inlet and outlet of a twin-entry radial turbocharger turbine rotor has been measured using a laser-2-focus velocimeter (L2F) under steady flow condition, both at design and off design operating conditions. The test condition has been extended from full admission to a full range of partial admission condition from zero to maximum flow in each inlet of the twin-entry volute. By measuring the same point in the flow from another angle, it is possible to investigate the presence of the axial component of velocity at the rotor inlet, particularly under partial admission conditions. From these detailed measurements, it is possible to obtain new insights into the fluid dynamic processes of the turbine over varying operating conditions, particularly for partial admission conditions.

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The aerodynamic performance of a horizontal-axis wind turbine has been calculated by applying strip and cascade theories. The results obtained by these theories have been compared with the experimental and other numerical data. It has been found that the cascade theory predicts better results at low tip speed ratios.

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We conducted a series of experiments in order to investigate the feasibility of active surge suppression in life-size industrial machines. The diameter of the impeller used in these experiments was 250 mm. These experiments were performed with closed-loop and open-loop compressor systems with a control valve on the suction pipe, both of which differed from Epstein's model. Active surge suppression was possible in both compressor systems. The action of the control valve was observed to suppress flow fluctuations from the dynamically unstable equilibrium point at every instant. We also numerically analysed the open-loop case. The action of the control valve was modeled by on-off throttle control and the compressor system was analyzed numerically using a lumped parameter model. This numerical analysis successfully reproduced the behavior of active surge suppression.

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Solutions for the imbalance response and stability of squeeze-film-damped nonlinear rotor bearing systems are presented. The rotor imbalance response is approximated by a trigonometric series whose coefficients are determined using a collocation method together with a nonlinear least squares regression. To improve numerical efficiency, the number of nonlinear equations for iterative solution is reduced to that corresponding to the number of nonlinear supports. A linear polynomial predictor is used to provide initial values for the iteration and, to ensure continuity through critical points, an arc-length continuation algorithm is used. To investigate the stability of the solution, the Floquet transition matrix method is used with an approximate transition matrix computed using a rectangular ripple method. Numerical examples are given for an eccentric squeeze-film-damper-mounted rigid rotor.

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Transition boiling heat transfer is studied by carrying out an experiment on steady pool boiling of water under atmospheric pressure and saturated condition on a horizontal copper disc 10 mm in diameter. Bubble (vapor mass) departure diameter and frequency were measured using high-speed video movies and an impedance probe, and they are well correlated as a function of heat flux. It is found that in transition boiling, heat transfer characteristics at low and at high wall superheats are considerably different. The macrolayer evaporation model, which was first proposed by Katto and Yokoya in 1970, is revised on the basis of nucleation heat flux previously measured by the authors to explain the transition boiling heat transfer at low wall superheat.

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This work is one of the fundamental steps in the study of thermal radiation characteristics of metallic materials in actual industrial or natural environments. A new algorithm is presented for modelling the microstructure of a rough surface. A superimposition technique is introduced to realize the concept of three-dimensional continuous self-similar microgeometry. Scattering of radiation on the surface is described on the basis of an electromagnetic theory of diffraction. The proposed method is examined by means of a numerical calculation and a bidirectional reflectance measurement.

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The measuring beam rays of real-time holographic interferometry curve due to light deflection in the temperature field of interest, and this results in a significant error in the temperature measurements. In this paper, a numerical simulation is performed to make clear the deflection characteristics of the incident measuring rays passing through the thermal boundary layer developing along an isothermally heated plate. Then the additional fringe order shift and fringe position displacement due to light deflection in holographic interferometry are calculated, and compensation for the deflection measurement uncertainty is made by analyzing the fringes of real holographic interferograms. The validity of this compensation is confirmed by experimentation on the combined free and forced convection flow fields in the thermal entrance region of a horizontal rectangular duct with a constant wall temperature. As a result, this compensation method is found to be useful in improving the measurement accuracy.

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The porosity of the near-wall region is higher than that of the core region in a porous insulating layer. Then the buoyancy-driven flow will be channelled along the wall of the layer. Considering such an inhomogeneous porous multilayer consisting of a thin fluid layer and a homogeneous porous layer, and proposing an extension of the Beavers-Joseph condition, a theoretical analysis is made on the buoyant channelling flow to clarify the effect of flow and thermal resistance near the wall on heat transfer characteristics. It is shown that heat transfer is generally enhanced by enthalpy transport due to the channelling flow ; however, in the weak convection region it is reduced by the thermal resistance near the wall. Discussion is also focused on the critical thickness of the effective fluid layer to eliminate the effect of the enthalpy transport.

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The conventional swirl-type injector used as a single-point injector has some faults, in that at low fuel flow rate it becomes difficult to generate a thin fuel film, and spray characteristics deteriorate. A new type of single-point injector is proposed in this paper to solve the above problem and to improve its atomization performance. The newly designed injector is of the impingement type. Liquid fuel jets impinge on the solid wall and form thin liquid films ; then they are issued from the injector. This type of injector has the following advantages. The impingement-type injector can generate a thin liquid film even at a lower liquid flow rate. The liquid film issued from the impingement-type injector is thinner and spreads out more widely. The droplets generated by the disintegration of the thin liquid film are finer. The azimuthal mass flux distribution of droplets is more uniform. The upwash generated by the impingement of the films promotes film spreading. However, a large upwash checks the uniform azimuthal distribution of droplet mass flux.

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This paper discusses the atomization mechanism of a spray injected into a low-pressure field, as the focus of an injection system in a suction manifold of gasoline engines. Pure liquid fuel, which is n-Pentane or n-Hexane, is injected into a quiescent gaseous atmosphere at room temperature and low pressure through a pintle-type gasoline injector. Fuel sprays are observed through photographs with varying back pressure, and the changes in spray characteristics with the back pressure below atmospheric pressure are examined in detail. In particular, in the case of back pressure below the saturated vapor pressure of fuel, the atomization mechanism is discussed from the viewpoint of the flash boiling phenomenon. Spray characteristics can be obtained with the pressure difference between the back pressure and the vapor pressure, corresponding to the intensity of the flash boiling, for various fuels.

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In order to elucidate the atomization process of a liquid jet across a high-speed airstream, the spatial distribution of the liquid, the drop diameter and the drop trajectory were calculated. In the calculation model, a liquid column is not incorporated. The drops ejected from the injector have the same velocity V_l, but different drop diameters, which are defined by the volume distribution of the drop size. The ejected drop is broken up by the airstream. The calculated spatial distribution of the liquid was in good agreement with the measured spatial distribution of the liquid. The trend of the calculated drop diameters agreed well with the trend of the measured Sauter mean diameter. The drop diameter decreased rapidly near the injector, especially along the outer line of the spray.

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The purpose of this study is to investigate the method of removing the NO_x contained in combustion exhaust gases by nitrogen plasma injection. Removal characteristics of NO_x are studied under the Zeldovich mechanism. First, the temperature and velocity distributions of the plasma wake were measured along the plasma jet axis. Optimum flow rates of plasma N₂ gas and simulated exhaust gas were determined after consideration of stable plasma operation and the formation of N atoms in arc plasma. Secondly, the simulated exhaust gas (N₂+O₂+CO₂+NO) was mixed with N atoms produced in the N₂ plasma. The Zeldovich reactions for excited N atoms with NO and O₂ will take place. The effects of O₂, CO₂, and H₂O on the reduction of NO_x were studied experimentally. The NO_x removal ratio of 40 to 50% is observed under the condition of O₂ concentration of 3 to 5% and the plasma power of 600 W ; CO concentration generated in the exhaust gas is about 300 ppm. The removal ratio η is highest for a low reaction temperature of less than 500 K. The value of η changes from 100 to 60% due to the addition of H₂O to gas. However, the recovery of the removal ratio is achieved by changing the gas injection site to plasma, as a result of the decrease of OH radical formation. Retention time required for reaction is less than ten milliseconds.

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The effect of the dimensions of a prechamber was researched using a medium-sized single-cylinder engine. The air-fuel ratio, A/F, in the prechamber changed quickly, when only gas was supplied to the prechamber. The amount of gas supplied, ignition timing, and A/F in the main chamber were affected by A/F in the prechamber at ignition timing. A larger volume ratio of the prechamber results in a higher level of NO_x emission and lower level of heat consumption. However, optimizing the dimensions of the hole results in improvement in the heat consumption level while maintaining the same level of NO_x emission. Suitable A/F in the prechamber allows the engine to function, but this is also the source of NO_x. The volume of the prechamber must be small and the dimensions of the hole must be optimized.

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Irregular combustion is the major disadvantage of two-stroke cycle S. I. engines under low load conditions. This study was intended to find the cause of the irregular combustion and to suggest ways to deal with this problem. The effects of intake air temperature, skip firing and fuel-injection timing on the cycle-to-cycle combustion variations in a two-stroke low-pressure air-assisted fuel injection S. I. engine were investigated. The cylinder pressures of successive engine cycles were recorded for statistical analysis. The intake air temperature was changed from 35 to 70°C. The residual gas concentration was changed by skip firing strategy, with skip 0, skip 4, skip 5 and skip 6. The air-injection timing which determines the fuel-air mixture injection timing into the cylinder was controlled by an electronic control unit. The items of injection timing were changed from 180 to 230 deg-ATDC. Results showed that the effects of intake air temperature, residual gas concentration variation and air-injection timing on combustion variations were significant. Raising the intake air temperature, reducing the residual gas content and adjusting the air-injection timing have greatly decreased cycle-to-cycle combustion variations and unburnt HC emission. The optimal values of coefficient of variation of indicated mean effective pressures (COV_imep) exist under the effects of the above parameters.

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The pilot injection pattern was optimized, and some effects of pilot injection on combustion and exhaust emissions were investigated using a single-cylinder DI diesel engine. The results are as follows. (1) In order to avoid the increase of smoke, both a small-hole-diameter nozzle and very accurate control of pilot injection quanTITY and pilot-main interval are essential. These improve the atomization of the pilot fuel and the air entrainment into the main spray. (2) With pilot injection, NO_x is not reduced at the injection timing of TDC but is gradually reduced at more retarded injection timing. This is because the main combustion is accelerated at early injection timing but is decelerated at retarded injection timing, due to the promotion of ignition. (3) The effect of pilot injection on NO_x reduction is generally small ; however, pilot injection well prevents HC increase under light-load, injection-timing-retard conditions.

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In order to utilize exhaust gas energy effectively, various engine systems equipped with exhaust gas turbines have been proposed. Since their performance depends greatly on the matching technique, the authors have been developing a method of optimizing these systems on the basis of mathematical treatments. The purpose of this paper is to describe a mathematical optimization procedure and to show its application to a turbocharged engine. This method consists of three steps : (1) choice of parameters representative of turbine and compressor characteristics, (2) efficient estimation of their behavior, (3) parameter optimization. The method was shown to have the capability of optimizing the engine system efficiently and to possess both flexibility and generality.

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