The gas-wall interaction is investigated for the Couette flow and the thermal problem between two walls whose temperature are different each other. The wall consists of platinum molecules and has grooves in molecular scale. The method of analysis is based on the molecular dynamics as well as DSMC method. The gas is taken to be argon. The slip and jump coefficients, tangential momentum and energy accommodation coefficients are obtained at the grooved wall surface whose temperature is 300K.

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In has been confirmed that a turbo-molecular pump (TMP) coated with SiO_2 gives a higher compression ratio than a non-coated pump by a previous experiment. In order to investigate the effect of the surface roughness on the pumpling performance, the surface roughness was modeled by statistically located circular cone peaks and dimples of the same base radius and various base angle. The actual surface roughness of the blade was measured by SEM, and then the obtained angle distribution was used for the roughness model. The 3D Monte Carlo simulation for SiO_2 coated TMP was done using the proposed surface roughness model. The calculated maximum-compression ratio was compared with the previously measured values and 2D calculated results. The present results showed almost the same values as the experimental ones, and agree well with the 2D calculated results.

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The new intermolecular collision scheme is developed to obtain an excellent result even if cells are lengthened in the DSMC calculation. In the new scheme, the velocity of one molecule of a collision pair is modified before and after a conventional collision calculation, assuming that velocity distributions in all flowfield are in local equilibrium with some temperature and flow velocity. The new collision scheme is applied to an one-dimensional normal shock wave, a two-dimensional vortex in a square cavity, an axisymmetric supersonic free jet, and a three-dimensional supersonic jet, respectively, and its effect is confirmed.

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Chemical vapor deposition (CVD) process composes a complex system, where chemical reaction and heat and mass transfer interact with each other. And these macro-scale phenomena are deeply related to the micro-scale mechanics. Hence multi-scale analysis is required to understand these complicated phenomena. First, the new pair potential model of SiH_4 molecule was constructed using ab initio molecular orbital calculations. Next, many binary collisions between SiH_4 molecules are simulated by classical trajectory calculations with various initial conditions. Through the statistical analysis, the total collision cross section model and the probabilistic scattering model for polyatomic molecules are constructed. At last these models are introduced into the DSMC simulation and the thermofluid structure in the Jet-CVD reactor is calculated.

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The direct simulation Monte Carlo (DSMC) method is widely used for simulations of rarefied gas flows. To make a vibrational relaxation model of diatomic molecules for the DSMC method, the collisions of diatomic molecules are investigated numerically. The collision cross section for vibrational relaxation can be described as a function of the relative translational energy and the rotational and the vibrational energy level of each colliding molecule. Thus the collision cross section could be evaluated with the Monte Carlo integration for these parameters. To achieve this idea, a lot of collisions with appropriate initial conditions should be calculated and analyzed statistically. A collision is simulated with the Semiclassical approach in which the vibrational motion is treated quantum mechanically and the rotational and the relative translational energies are treated classically. For the comparison of methods, the Quasiclassical approach is applied. The simulation by this method is same as that by the classical method, and the obtained vibrational energy is discretized to the quantum level.

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Recently, plasma reactor using multipole magnetic field is watched with keen interest. The multipole magnetic field makes plasma low pressure, high density and uniform. We present the effect of multipole-magnetic field for plasma reactor, and research the better way to confine electrons.

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Quantum theory of distorted-wave Born approximation (DWBA) can be applied to the electron impact ionization, i.e.(e, 2e) process. In particular, the data of cross section for the electron-atom ionization collision are theoretically predicated by DWBA, and it covers the electron energy level in materials processing. Furthermore, electron energies and the angle between two scattered electrons after the collision can be obtained. They are quantum mechanically measurable, and the quantitative comparison of them between the theory and the experiment can be made in detail. Previous works often omitted the exchange term of the basic equation after the partial wave decomposition of Schrodinger equations, and it results the serious disadvantage from the viewpoint of engineering. In the present paper, novel method for numerically solving the basic equation in electron-hydrogen scattering is presented based on the iterative methods. The validity of the present study is discussed based on previous similar works.

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Recently, the micro/nano devices in the research area of life science, e.g. development of DNA chips or μ-TAS, have received considerable attention. The nanoscale fluids engineering research is very important to develop the industrial products, which must be designed from the microscopic viewpoint, because the fluid phenomena in such small devices are governed by the molecular force, coulomb force and so on. The behavior of nanodroplet provides the basic interests in nanoscale fluid engineering. There are a huge number of classical studies based on Navier-Stokes equations on the drop formation mechanism, mass transfer characteristics and interfacial phenomena, e.g. oscillation or breakdown. The comparison of the microscopic research with the classical results must be very important and interesting. In the present paper, the interfacial phenomena of nanodroplet in vacuum, in the vapor, and in different gas are numerically analyzed by the molecular dynamics simulation. The molecular diffusion and the formation of so-called the interfacial layer at the interface are quantitatively investigated as the basic knowledge in nanoscale fluids engineering.

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The mathematical model for discharge in lithium ion batteries is developed based on novel multiphase fluid model. The phases of lithium, lithium ion, negative ion and the electron are considered in the model. Maxwell's equations for electric field and Butler-Volmer equation for electrochemical reaction are also included. The numerical code based on implicit SOR scheme is developed and the numerical solutions of the discharge characteristics are successfully obtained for various operating conditions. Furthermore, the comparisons of the discharge characteristics between experimental and numerical results are made in detail. They are in good agreement from the viewpoint of engineering applications. Consequently, it is found that the nanoscale multiphase fluid model and the numerical scheme proposed here are useful enough for practical computational design of the lithium ion rechargeable batteries.

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Numerical study of high-speed submerged water jet accompanied with cavitation bubbles requires an adequate model that is capable of describing locally high pressures and the phase change due to strong collapse of bubbles. For this purpose, a system of averaged equations for two-phase bubbly flows is derived, where a surface average pressure of liquid is introduced in addition to volume average pressures taken for gas and liquid phases respectively. The surface average pressure is connected to the volume average pressures through the momentum jump condition. The mass and momentum transfers across the interface by the phase change are also taken into account, although a liquid temperature is assumed constant.

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An abrasive water suspension jet (AWSJ) has a greater capacity for drilling and cutting than the abrasive water injection jet (AWIJ). The drilling capability of the AWSJ under submerged condition decreases steeply with the increase of the standoff distance. In order to expand the effective standoff distance of the AWSJ under submerged condition, a sheath AWSJ nozzle is proposed and the drilling capability of the sheath AWSJ nozzle is clarified through drilling tests with specimens of stainless steal.

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Cavitation erosion was compared between venturi tube and cavitating jet methods. It was found that the erosion by cavitating jets occurs 400 to 1000 times as fast as that by the venturi tube, thus the cavitating jet method is effective for the acceleration test. The exponent of the relation between MDERmax (mean depth of erosion rate) and flow velocity is 2.3 to 3.3 for venturi tube and is 6.5 for cavitating jet, which agrees with that of the relation between ΣFi^2 and flow velocity. It was concluded that MDERmax of venturi tube can be estimated from the extrapolation of the relation between ΣFi^2 and MDERmax which was obtained for the cavitating jet test.

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Simultaneous damage tests of cavitation erosion and slurry wear were carried out for Stellite, SCMnH11,TiNi shape memory alloy, and SUS304. The volume loss rate of the simultaneous damage is higher than that of slurry wear without cavitation for SUS304. On the other hand, the volume loss rate of the simultaneous damage is lower for satellite and SCMnH11,thus deceleration phenomenon appears. The simultaneous damage has no effect for TiNi shape memory alloy which subject to phase transformation due to cavitation bubble collapse pressure. It was concluded that work hardening by cavitation bublle collapse pressures is responsible for the deceleration phenomenon by simultaneous damage.

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We performed experiments to clarify mechanism of cavitation erosion at the exit of a long orifice. In order to find this mechanism, we used a high speed video camera. As the result, we observed bubble collapses near the exit of the orifice when flow condition was oscillating. So bubble collapses due to the oscillation might cause the first stage erosion at the exit of the orifice. Using the orifice which had the tapered exit, we observed that bubble collapsed near the exit and after that bubble collapsed at the upstream of the taper like a chain reaction. The propagation speed of the bubble collapses agreed well with sonic velocity in two phase flow. So this bubble collapse mechanism could be concluded as follows : shock wave was generated by bubble collapse near the exit, then it propagate upwards, cosequently it caused bubble collapse at the upstream.

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It is known that cavitation erosion cause to break the parts of fluid machinery or damage the tissue of the body during medical ultrasound, for example, ESWL : Extracorporeal Shock Wave Lithotripsy. But if cavitation behavior can be analyzed and controlled actively, we are able to utilize cavitation as a transducer, which can concentrate energy in a very narrow area. And this cavitation control has the possibilities to be applied in engineering and medical field. In order to analyze cavitation behavior in ultrasound field, we conduct experiments and numerically simulate the dynamics of bubble cloud in detail, and we obtain the following conclusions. We build the method to concentrate cavitation cloud only in a small region with high frequency ultrasound and oscillate and crush the cloud with low frequency one near the natural frequency of it. And it is possible to break an object in a narrow area by this method.

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Simulation of bubble cavitation is done to check whether the cavitation has enough potentiality to activate chemical reaction inside the bubble. This simulation algorithm is composed of two parts. The first part is for simulating bubbly flow is a nozzle. And the second part is for simulating Oxy-Hydrogen chemical reactions those may occur inside bubble if the condition is proper to activate the chemical reactants. These two parts of simulations are coupled together with variables, for instant bubble pressure, bubble temperature, mole molecules of gas inside bubble and heat emitted by reaction. The results show that chemical reaction can be activated by violent collapse of cavitating bubble under a certain condition.

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Since probabilistic cavitation has to be inherently specified by several stochastic parameters and generally consists of several types of cavitation bubbles, the cavitation tunnel has to satisfy several necessary conditions in order to specify the cavitation aspects definitely. In this paper, therefore, we try to clarify the tunnel performace such as, the velocity distribution, the boundary layer aspects, the void fraction around the cavitation and the vorticity distribution within the test section of our SIT cavitation tunnel, that are directly related to the cavitation aspects, by means of an PIV technique, by which the velocity distribution, the vorticity distribution and the cavitation aspects are able to obtain easily and simultaneously.

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In the present study, the incipient mechanism of traveling bubble cavitation and the relation with the water quality were investigated experimentally. A nozzle-type venturi tube was used to make a single bubble cavitation. The incipient and growing process of a single bubble was experimentally observed at various positions of the nozzle throat. At the same time, a rapid change in bubble diameter during the collapsing period was seen compared with that of the growing period. The collapsing pattern of the various shapes was confirmed by the high-speed video observation. The action of rebound motion as well as a micro-jet and a torus deformation of bubble were observed. The inception of a single bubble cavitation was measured in different dissolved oxygen contents, and it was confirmed that the count rate of bubble inception varies stochastically.

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An analytical method for the steady cavitation in turbomachinery is proposed under the assumption that stream surface is rotationally symmetric. The analysis on stream surface is performed by a singurality method based on closed cavity model and is combined with the analysis on meridian plane through the circumferentially averaged velocity. The present method is applied for a flat-helical inducer and the characteristics of alternate blade cavitation and three-dimensional effects on cavitation are discussed in comparison with the results of the analysis of two-dimensional flow.

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Unstable cavitating flow phenomena through three-blade cascade, which is similar to the rotating cavitation occurring in turbomachinery, are simulated numerically. A numerical method employing a locally homogeneous model of compressible gas-liquid two-phase medium is applied to solve above cavitating flowfields. Since the present method permits us to treat rather simply the whole flow fields inside and outside the cavity, it is possible to macroscopically analyze unsteady phenomenon with a long time evolution. From calculated results, we get a cavitation characteristics curve of the cascade, and discuss an aspect of propagation of uneven cavitation.

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A bubble cluster formed by the bubble concentration near the wall in bubbly two-phase flow with sub-mm diameter bubbles is experimentally investigated in a rectangular channel for upward flows. The rising velocity and behavior of the cluster are measured by the PIV (Particle Image Velocitimetry). By adding the surfactant, the coalescence of bubbles is prevented and small bubbles about 1mm in diameter are uniformly generated. In the two-phase flow with sub-mm diameter bubbles, the horizontal bubble clusters 20-40mm in length are formed near the wall because bubbles are strongly accumulated by the lift force and they slide up along the wall. Consequently, the cluster shape was changed by the junction of bubble in the center of cluster and by the separation in the both end of cluster. These results are caused by the difference of the rising velocity between the cluster center and the both end.

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The formation of air bubbles from a injection nozzle submerged in a water/glycerol solution inside a cylindrical tube is investigated by the methodology of the nonlinear time series analysis. It was found from the bifurcation diagram of bubble interval that the period doubling bifurcation occurred by the increase in gas flow rate. Correlation dimensions were estimated from the nozzle pressure fluctuation, and the results indicate that the bifurcation from periodic orbit to chaos occurred in high air flow rate region. It was shown that the correlation dimension could detect the transition of the pressure fluctuation dynamics that could not be detected by mean values and standard deviations.

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We investigated the injection of microbubbles through a micro capillary tube. The number density of the injected microbubbles was controlled with an actuator. These microbubbles are planed to be used for the laser trap or laser manipulation of microbubbles. In the laser trap, we use the laser cone that is made by rotating the laser ring. We succeeded in injecting microbubbles with the velocity of about 150μm/s. We simulated the trajectory of microbubbles injected through the capillary tube until they trapped by the laser cone. The optical force, buoyancy and viscous drag force were taken into account in the simulations. The simulations showed that the microbubble of 5μm diameter, which was injected near the axis of the laser cone, was trapped below the focus of the laser beam if the velocity of bubble injection was slower than about 500μm/s.

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The characteristic of generating the micro bubble by the strong swirl jet from the orifice nozzle is studied experimentally and theoretically. For the evaluation of the aspect of micro bubble generation, a method using the transmittance of the light is used in the water tank with a circulation system. By the method the parameters of the average diameter of micro bubbles, the bubble generation rate and the number density are obtained, and the characteristic of the micro bubble generator can be easily evaluated. The mechanism of the micro bubble generation is examined on the basis of the momentary photography and numerical simulation, and it is shown that the miniaturization of the bubble is caused by the division of a cylindrical large bubble in the two opposed flow in the orifice exit.

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We experimentally investigate the velocity of free falling powder jet and entrained air near the hopper exit. A phase-Doppler anemometer(P.D.A.) is used for the measurement of their velocities. We found that the relative velocity between particle and air is so small that the center-line velocity of powder jet is close to the falling velocity of a single particle in disregard of the fluid drag. We obtaind that the dimensionless velocity profiles of powder jet are similar and independent of the falling distance. The volumetric flow rate of entrained air is increased with an increasing falling distance.

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The micro-structured water-repellent surface has been reported to reduce friction coefficient. The surface has been microscopically observed in this study to clarify whether it holds air layer that is believed to cause drag reduction on the surface. The observation certified the existence of the air layer and its state is affected by some condition such as flow rate or air-solubility of the fluid. In air-saturated water, the air layer exists for hours during the experiment. The air-saturated water flow enhanced the stability of the air layer, while degassed water quickly penetrate the microscale concave on the surface.

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When the liquid for cooling is sprayed into supersonic flows with high temperature, it is important to understand cooling effects by evaporation on the flows. It is required that the spray used for this purpose should be miniature to make the effects on the flow as small as possible and the droplet discharged should be evaporated easily. The foundational experiments are done to develop the atomizer which fulfills these conditions. In the present study, experimental research on figures and capacity of swirl chamber, and the figures of jet nozzle etc. is performed, and the design parameters of spray to get the desirable mist condition are clarified.

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The "Magic Ball", newly developed by Moritex Co. in Japan, is considered to be an excellent advertising medium. The "Magic Ball" is composed of a vertical plate with radiation elements, a horizontal basic plate and a balancing weight. The radiation elements are controlled electronically using a computer to project advertising letters and figures on the sorrounding globe. The aerodynamic drag forces of the composed parts are measured using a wind tunnel. The sound noise level, caused by high-speed rotation of the composed parts in the "Magic Ball", is measured and discussed for various forms of the composed parts. It is found that the attachment of small cylinders decreases aerodynamic noise sharply. The optimum forms of the composed parts realize the reduction of sound noise level by 3dB comparing with the prototype "Magic Ball".

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The sound field in a rectangular duct with slits is computed by a finite difference method and the transmission characteristic is measured. The slits are duct expansions located on two opposite side of a duct with short axial length. Both the computed sound attenuation and the measured one occurred at a specific frequency, that is, resonance frequency. The resonance frequency for the slits of the same depth almost coincides with the second order cut-off frequency in the direction of slit depth. The resonance frequency becomes to be lower according to the deeper depth of slit. The resonance frequency for the slits of different depth is close to the resonance frequency of the slits with the averaged depth. The computed results are in good agreement with experimental data.

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Finite amplitude standing wave induced in closed tube with cross sectional area change has been investigated by experiment. The effect of tube shape on getting high amplitude pressure waveform at closed end of the duct and the frequency responses has been discussed. Three kinds of tube namely conical, exponential and 1/2 cosine shaped were chosen for the experiment. The tubes were filled with HFC134a at normal atmospheric pressure and temperature. Results show that the peak-peak pressure amplitude increases with the increase of acceleration amplitude, but the amplitude and the presence of micro-shock varies with the tube shape. The frequency response curve in conical and exponential tube shows hardening and hysteresis behavior at high accelerations, however the response curve in cosine resonator is stable, as it does not show hysteresis and frequency shift behavior. Therefore, the 1/2 cosine tube is best candidate in order to design acoustic compressor.

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A system and a procedure shown in a previous report, which can identify location of sound source by near-field acoustic holography method using sound fields apart from the source measured with a small pressure transducer in a uniform flow, was applied to detection of a discrete frequency noise, DFN. It has been verified that three-dimensional distributions of sound fields can be estimated fairy well with this system from the tests for pressure fluctuations on a circular cylinder. Moreover, sound pressure distributions over the entire surface of a flat plate aerofoil with various boundary layer manipulations were estimated. As a consequence of additional consideration with an aid of experimental data of pressure fluctuations on aerofoil as well as coherent flow structures near it, four different types of DFN generating mechanisms have been proposed.

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Static pressure fluctuation is a basic flow variable in turbulence, but it is perhaps a least understood quantity. We tried to measure it using a condenser microphone probe. The sensor is fitted with a tubing, as a pressure duct and is inserted into the flow domain in such a way that the axis of the microphone body is aligned with the mean stream. The frequency response of the system is distorted by the Helmholtz-resonator response of the tube and the sensor cavity. The resonance effect has been corrected for by processing the measured signal in the frequency domain, and its maginitude has been quantified for the pressure fluctuation and the pressure-velocity correlation measured in a wake flow behind a cylinder.

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This paper treats the experiment of the performance of a horizontal axis wind turbine with an extra small diameter rotor in front of the main rotor. In this experiment, the wind turbine of rotor diameter 482mm, NACA-4415 airfoil is used as a main rotor and a small rotor of diameter 276mm with the similar airfoil section to the main rotor is installed in front of the nacelle. The results show that the power output of double rotor wind turbine is greater than the normal rotor wind turbine.

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There is a continuing trend towards building large wind turbines, especially for offshore use. Large blades will experience a wide range of Mach numbers. CFD is a promising tool for accurate wind turbine performance prediction. It is necessary to develop a CFD code that can solve incompressible and compressible flow simultaneously. A compressible Navier-Stokes code with an approximately-factored algorithm is extended for flow at low Mach numbers using the method of local preconditioning. The turbulent flow around the NREL S809 airfoil is calculated for a wide range of Mach numbers. For low Mach numbers the convergence rate and accuracy are significantly improved compared to the calculation without local preconditioning.

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Performance of Vertical-Axis Wind Turbines (VAWT) are numerically investigated by using vortex methods. Although VAWT have several advantages in comparison to the conventional propeller-typed wind turbines, they are not popular as commercial products, because of the weakly self-starting problem. In this study, we attempted to predict instantaneous turbulent flow-field around VAWT and estimate its aerodynamic performance. The result shows the aerodynamic performance is almost the same as the conventional wind turbines. Moreover, vortex methods are suitable method for performance estimation of wind turbines.

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The merit of a system consisting of a roof-top fairing and an air-turbine integrated within the fairing, which were wholly mounted on the cabin roof of a container-truck, was evaluated by model experiments in a wind tunnel. The turbine absorbs the air power passing through an internal air duct from the high-pressure front opening to the top exit in the low pressure region. It aimed both the aerodynamic drag reduction by the fairing and the power generation by the turbine. The experiments demonstrated that the system could contribute much to the economy of the truck.

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This report describes a prototype wind turbine for wind power generation. This wind turbine is designed to fit in both lower wind and urban circumstances like Amagasaki city. Therefore, it belongs to drag type rotor with multi blades. After six months measurements of wind speed and wind direction, it is located horizontally toward the north-northeast. The power and torque properties of this rotor proved to be similar to those of a cross flow rotor through experiments with an open wind tunnel. And it attains activation in the wind velocity of 0.3m/s and starts generation in 0.7m/s.

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The small-scale systems have an advantage on net power extraction under fields wind conditions in introducing the variable speed operation for adequately utilizing wind energy. This is because of the superior dynamic characteristics of the small-scale systems. Thus, in order to extract demanding electricity, it is necessary to adopt the parallel operation using plural wind turbines which have the appropriate system scale matching the wind condition. The purpose of this study is to propose the operating method of the parallel systems using two Darrieus-Savonius hybrid wind turbine-induction generators for higher power extraction. This paper discusses the load control method at the starting and the stopping. The computed results shows that the system under our operating scheme of two turbines has the fine starting and stopping behavior.

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The numerical method for analyzing a fixed terminator type of wave energy conversion device is described under the condition that the linear water wave theory is applicable. The method is proposed in order to calculate the device characteristics of an air chamber. It uses the flow rate and the gage pressure in the air chamber directly, because the interaction between oscillating water column and the turbine is controlled only by the flow rate and the pressure drop through the turbine in this system. It is confirmed that the solution gives good agreement with the experimental data.

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To conserve natural ecosystem and coexist with nature, this paper proposes a new type hydraulic turbine, named "Gyro-Type Hydraulic Turbine" by the authors, suitable for shallow streams with high velocity in mountain torrents and/or rivers, accompanying with the principle of the rotor works and discussions of the model test results. This hydropower unit scarcely disrupts the natural streams and environments, that is, it is not necessary to start the public works on a large scale because the generator connected with the shaft can be easily set on the simple stand over the water level. The rotor has the self-motive power and is driven by the drag force of the blade facing to the downstream at the low rotational speed. With the increase of the rotational speed, the rotational torque comes to be successfully caused by the lift forces of the blade not only facing to the upstream but also facing to the downstream.

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The present authors are carrying out the research on the unstable flow occurred in a mixed flow vaneless diffuser system. In the experiment, a high-speed mode of rotating stall was measured. In order to clarify the cause of the high-speed mode, the instability of swirling flow in a pipe was examined using a test equipment composed of a swirling flow generator, a straight pipe and a hub. Main results are as follows. In the case without the hub, the high-speed mode was observed for relatively short pipes. In the case with the hub, the same mode was measured for the short hub with the small diameter. It was theoretically clarified that the high-speed mode measured was based on the rotation of a vortex core. A lower-speed mode can be explained by the small perturbation analysis which assumed a radial mode.

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A transient phenomenon of stall inception in an axial compressor was investigated experimentally with an array of 4×6 pressure sensors mounted on the casing wall. The precise distributions of instantaneous casing wall pressure was obtained by a newly-developed 'Synchronous Field Measurement'. At stall inception, the temporal variation of the casing wall distribution reveals the development of the leading edge separation and the separation vortex.

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Three-dimensional and unsteady flow phenomena due to the breakdown of the tip leakage vortex in a transonic axial compressor rotor NASA Rotor 37 have been investigated by an unsteady RANS simulation with a two-equation (k-ω) turbulence model. The simulation shows that the bubble-type breakdown of the tip leakage vortex is caused by the interaction between the tip leakage vortex and the shock wave. The interaction gives rise to self-sustained flow oscillation even at near-design point.

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In the load rejection test of Kazunogawa pumped storage P. S. in Japan, an abnormal axial thrust occurred in a high-head reversible pump-turbine (412 MW and 714 m effective head). The rotating parts including a runner moved 4 mm upward in the axial direction. After taking several countermeasures, this machine is now operating without any problem, but the mechanism of transient axial thrust is not yet clear, though such a transient up-thrust has long been known. The present study is thus aimed to determine the reason why such abnormal axial thrust is caused at the transient operation and how to reduce abnormal thrust. Here adopted is a theoretical approach which has been proved to give satisfactory results in predicting pump axial thrust.

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Many rocket launch failures are caused by engine problem, especially by the propellant feed system problem. Analysis of transient or unsteady characteristics of turbopump system is necessary on conducting rocket engine stability analysis such as POGO analysis. Dynamic characteristics of cavitating inducer isn't governed only by cavitation compliance defined as the ratio of cavity volume change rate to inducer inlet pressure change rate, but also by mass flow gain factor defined as the ratio of cavity volume change rate to inducer inlet mass flow change rate. This paper provides a new dynamic model of rocket engine LH_2 feed system and gives some stability analysis results.

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In the present study, the head/discharge characteristics of a centrifugal pump depending on the direction of partial load operation have been investigated through calculating internal flow. Based on the hypothesis of axisymmetric flow, the numerical simulation on the incompressible turbulent flow has been carried out for partial blade-passages with periodic boundary conditions. In the numerical calculation, the data previously calculated at a little more or less discharge are given as the initial condition. In the numerical results at partial flow operations the pump has the large backflow and recirculation regions in three locations, one of which is near the casing at the impeller inlet, another of which around the fins and the other of which near the central part of the diffuser. The scale of these regions varies steeply under two partial flow operation points as the discharge increases or decreases. As a result, the hysteresis loop appears in the head/discharge characteristics curve depending on the direction of partial load operation.

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In the range of very low specific speed (n_s≦100 [m, m^3/min, rpm]), performance of a centrifugal pump is much different from that of a normal n_s centrifugal pump and efficiency of the pump drops rapidly with a decrease of n_s. The purpose of this study is to make clear the internal flow characteristics and to obtain a basic knowledge of the pump performance. In order to examine the reason of unstable performance characteristics of a very low n_s centrifugal pump, the internal flow of a semi-open impeller is measured by PIV. The results show that large passage vortex and strong reverse flow at the outlet of impeller are formed at partial flow rate, and these vortex and reverse flow reduce a tangential velocity at the outlet of impeller and cause the performance instability. Slip factor of the semi-open impeller is higher than factor given by Wiesner.

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The cavitation flow in a low specific speed centrifugal pump was measured in detail. Eighteen Pressure transducers were installed in impeller vanes and unsteady pressure distribution over pressure side and suction side were captured. Cavitation characteristic was easily photographed in axial direction through transparent inlet volute casing and front shroud. At the BEP flow rate bubble cavitaion increases along the suction side while decreasing the NPSH. When bubble cavitation reaches the throat, wedge-like cavity appears at the pressure side and the head breakdown occurs steeply. At the high flow rate, wedge like cavity appears incipiently at the pressure side of the throat and head drops gradually. Single phase CFD shows good agreement with measured results at high NPSH.

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This paper describes about the effects of an inlet distortion on cavitation surge phenomena as well as the suction performance of an inducer. The inlet distortion is generated by a baffle plate located upstream of the tested inducer. As a result, the cavitation surge never occurred in the tested inducer with the baffle plate, while without the baffle plate it violently occurred under low flow rate conditions. The reason for this was well discussed using the measured cavity length variations due to the inlet distortion obtained by the visual observation

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A numerical study of the cavitation performance of 3-bladed inducer is performed. Calculations are made for two types of leading edge geometry using the commercial CFD code CFX-TASCflow, Cavity zone and cavitation behavior under different conditions are presented. It is shown that the cavitation zone and suction performance can be reasonably predicted.

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